1. Technical Field
The present invention relates to a method of manufacturing a printed circuit board.
2. Description of the Related Art
Since densification, thinness, miniaturization and electrical improvements are being demanded by semiconductor packages, a substrate is becoming thinner and an electronic component-embedded substrate in which an electronic component is mounted and protected is being increasingly used. However, as the substrate becomes thinner, there is a problem in that the supporting force of the substrate is decreased, and thus the warpage thereof is increased. In particular, an electronic component-embedded substrate is problematic in that, after it is encapsulated with an epoxy molding compound (EMC), it becomes warped because of the difference in the thermal expansion coefficient. Therefore, owing to the increase in the warpage of a substrate, it is difficult to accurately attach solder balls at the predetermined positions of the substrate.
FIGS. 1A to 1E are sectional views showing a conventional method of manufacturing a printed circuit board. Hereinafter, conventional problems will be described with reference to FIGS. 1A to 1E.
First, as shown in FIG. 1A, a strip substrate 1 is provided. Here, the strip substrate 1 may be an electronic component-embedded substrate on which an electronic component is encapsulated with an epoxy molding compound (EMC) 5. This strip substrate 1 becomes warped because of the difference in thermal expansion coefficient between the substrate and the EMC 5.
Subsequently, as shown in FIG. 1B, flux 2 is applied onto the strip substrate 1. Here, since the strip substrate 1 is warped, there is a problem in that the flux 2 is not accurately applied at the predetermined positions of the strip substrate 1.
Subsequently, as shown in FIG. 1C, solder balls 3 are attached to the strip substrate 1. Here, the solder balls 3 are attached using a jig. In this case, since the strip substrate 1 is warped, there is also a problem in that the solder balls 3 are not accurately attached at the predetermined positions of the strip substrate 1, and collect at the specific parts of the strip substrate 1.
Subsequently, as shown in FIGS. 1D and 1E, a reflow process and a singulation process are performed. In the reflow process, the solder balls 3 are fixed through heat treatment, and, in this procedure, the strip substrate 1 is additionally warped. Therefore, since the solder balls 3 are not accurately attached at the predetermined positions of the strip substrate 1 and the strip substrate 1 becomes additionally warped through the reflow process, when the strip substrate 1 is separated into unit substrates 4 through the singulation process, there are problems in that the solder balls 3 are not accurately attached at the predetermined positions of each of the unit substrates 4, and each of the unit substrates 4 is also considerably warped.
Further, the conventional method of manufacturing a printed circuit board is uneconomical because expensive equipment is required and equipment suitable for the strip substrate 1 must be provided whenever the kind of strip substrate 1 is changed. Although technologies for attaching solder balls using a screen printing process have been developed, these technologies are also difficult to be practically used when the strip substrate 1 is warped because the screen printing process premises that the strip substrate is flat.
Therefore, various solutions for decreasing the warpage of the strip substrate 1 have been proposed, but most of the solutions are problematic in that they require high production cost and are difficult to be put into practical use due to the change in the raw material and design of the substrate.